Dynamic behavior of the moisture near the soil-atmosphere boundary.

Dynamic relations between the moisture in the atmosphere and the soil are studied based on a field experiment. Sensors to measure the moisture in the skin layer near the atmosphere-soil boundary were developed and applied to the bare soil surface. The amount of moisture change in a shallow soil layer (less than 4 cm depth) was observed to be related to the rate of evaporation from the surface on the basis of daily averages. On the hourly basis, however, the agreements are poor. The soil moisture even at the small depth (-1 cm) began to decrease around noon although the evaporation started immediately after the start of insolation. The hydraulic diffusivity obtained from the phase difference of diurnal moisture variation is shown to vary with the volumetric water content of the soil.